Times of minimum light for TY UMa

Four-color light curves and radial velocities of this system were presented and simultaneously analyzed using the W-D code. It is found that TY UMa is a W-subtype shallow contact binary system (f=13.4%) with a mass ratio of q=2.523.

In order to explain the asymmetric light curve of this binary, a dark spot on the less massive component was employed. Our newly determined 31 times of minimum light, including those collected from the literature, have been used to analyze orbital period changes of TY UMa. The complicated period variation could be sorted into a secular period increase at a rate of d_p_/d_t_=+5.18(+/-0.21)x10^-7^days/yr, a 51.7yr periodic modulation (A_3_=0.0182days), and a very small amplitude cyclic oscillation with a period of 10.0yr (A_4_=0.0015days).